Cloud accounts · Google Photos
How much space will a Google Photos export need?
Short answer: About what Google Photos uses in your Google account storage, plus room to unpack. Takeout splits the export into archives; download them straight to an external drive or a few at a time if your Mac is short on space.
Roughly as much as Google Photos uses in your Google account storage — check your Google account's storage page for the figure — plus room to unpack the archives if you extract them.
Takeout lets you split the export into archives of a size you choose. If your Mac is short on space, download the archives straight to your external drive, or download a few at a time and move each one off your Mac. Google Photos can't be connected to Storage Studio right now, so Takeout is the route.